Where floppy discs are produced with data written thereon in large quantities, or indeed in any reasonable quantities, it is essential that the data should be written on the disc to conform to certain predetermined standards. For example, it is important that each track of data being written on the magnetic disc should be properly aligned on the disc, in other words, that the circumferential central line of each track should be within certain predetermined radial limits. It is also essential that the tracks of data should be written concentrically with the centre of the disc, and should not go beyond certain predetermined limits of eccentricity. Furthermore, it is important that the floppy disc should be driven by the disc drive apparatus at a speed which falls within certain predetermined limits during writing. It is also important that each track should be correctly indexed, in other words, that the beginning of each track of data should commence within certain predetermined limits of an index mark. The modulation and signal amplitude of the written data should also be within certain predetermined limits. Furthermore, it is important that the bits of data should be written in their correct relative position on each track. Each bit is assigned a window and each bit should be written well within its window. The test for this is normally referred to as a window margin test, and the window margin is the part of the window where no bits occur.
This requires that the disc drive which is writing the data should operate to write the data within the relatively tight predetermined limits. Should the disc drive apparatus fail to keep the characteristics within the predetermined limits, it is essential that the particular apparatus should immediately be taken out of production.
Unfortunately, the only known way for checking such disc drives is to take the apparatus out of production and physically check the various components and their relative alignment. For example, the alignment of the read/write head relative to the axis of the disc drive is precision measured and to ensure concentricity the rotational alignment of the disc drive shaft is also measured. The speed of the disc drive shaft is measured to ensure that the rotational speed of the floppy disc is correct during writing, and the relative position of the read/write head to the index window is also determined.
These tests require disassembling a considerable portion of the disc drive apparatus. It has been found in the past that where such apparatus is being reassembled after being tested, and/or after adjustments or corrections have been carried out, certain components may be inadvertently misaligned. This in many cases may not be discovered until a large number of discs had been written, which would ultimately have to be rejected. There is therefore a need for a method and apparatus for testing certain characteristics of magnetic disc drive apparatus which overcomes the problems of methods and apparatus known heretofore. Indeed, there is also a need for a method and apparatus for testing floppy discs to ensure that certain characteristics of the floppy discs are also within certain predetermined limits.